Ceramic pressure sensors are used widely in nearly every area of industrial measuring.
Ceramic pressure sensors can be designed as absolute pressure sensors which can measure the absolute pressure acting on the measuring membrane with respect to vacuum. They can be designed as relative pressure sensors which measure the pressure acting on the measuring membrane relative to a reference pressure that is applied to the pressure measuring chamber, such as the current atmospheric pressure. Alternately, they can be designed as differential pressure sensors with a measuring membrane disposed between two base bodies, while enclosing a pressure measuring chamber in each case, and the differential pressure sensors measure a pressure differential between a first pressure acting on a first side of the measuring membrane and a second pressure acting on the second side of the measuring membrane.
Today, ceramic pressure sensors are frequently designed as so-called capacitive pressure sensors. Capacitive pressure sensors have a capacitive converter that serves to determine by measurement the deflection of the measuring membrane depending on the pressure acting on the measuring membrane. Ceramic capacitive pressure sensors normally have an electrode disposed on a side of the measuring membrane facing the base body, and a counter electrode disposed on the side of the base body facing the measuring membrane. Electrodes and counter electrodes are normally metallic layers sputtered onto the inside of the measuring membrane, or onto the end face of the base body facing the measuring membrane. The counter electrode is normally electrically connected by a contact pin that is inserted into a straight bore running through the base body before sputtering the counter electrode. Electrode and counter electrode form a capacitor with a capacitance that depends on the deflection of the measuring membrane and which, for example, is detected by means of a capacitance measuring circuit, and which is assigned to a corresponding pressure measuring result via, for example, a characteristic curve which has been determined beforehand in a calibration method.
Today, ceramic base bodies as well as ceramic measuring membranes of ceramic pressure sensors are normally made from granules that are poured into a prefabricated mold. Then the granules are pressed by pressing a precisely-fitting, correspondingly shaped punch into the mold, and the pressed granules are sintered.
In this manner, simple geometric shapes of base bodies and measuring membranes, such as disks or cylinders, can be created with comparatively low production tolerances. The achievable production tolerances can furthermore be enhanced by subsequently precision-grinding the sintered bodies. However, the production of complex geometric bodies using this method is subject to narrow limits.
When pressing the granules, inhomogeneities can arise which can generate pores in the sintered body. The danger of inhomogeneities possibly occurring is all the greater the more complex the shape of the sintered body. Pores reduce the compressive strength of the sintered body.